Treating Giardia in Dogs

3D model of a Giardia protozoans

3D model of a Giardia Protozoan

Years ago, I bought an adorable little pied bitch. She arrived safe and sound, but she brought some extra friends with her – Giardia protozoans.

The Giardia parasite is a mysterious, annoying, tenacious little bug. It is a zoonotic disease, meaning it can effect both pets, and humans. Children are especially at risk of contracting Giardia (likely due to their habit of putting everything they find on the ground into their mouths).
Giardia causes diarrhea, and can also cause malabsorption of vitamins and nutrients. Giardia is difficult and expensive to diagnose definitively, and until recently required a very fresh stool sample and an inventive series of testing methods, including:
  • Being sure to examine a direct smear of the fecal sample (in hope of finding swimming trophs).
  • Floating the sample in zinc sulfate, a solution that has been found superior in getting Giardia cysts to float.
  • Staining the sample with some sort of iodine under the microscope to make the Giardia show up easier.
There is now a simple ELISA test available to simplify diagnosis, but since the giardia organism only sheds intermittently, several tests over an extended period of time can sometimes be required to obtain a definitive finding of Giardia.
Treatment of Giardia was even more complicated than diagnosing it. Until recently, the most commonly prescribed treatment was Metronidazole (trade name Flagyl®). Metronidazole was required in high doses, for an extended period of time, and was still only effective in just over 60% of all cases. Additionally, Metronidazole has some side effects in high doses, including nausea, neurological symptoms including head tilting and staggering, rapid eye movements known as “nystagmus“, and seizures (particularly in cats). Metronidazole also cannot be used on pregnant animals, as it has been linked to birth defects.

Like most breeders, I routinely worm my puppies, using the standard protocol of worming them every 2 weeks, starting at 3 weeks old. I now use a broad spectrum wormer which treats Giardia in addition to intestinal worms.

The brand we us is called Safeguard, and you can get it from almost any farm supply place in the USA. I get it from my veterinarian, since she makes it up into a suspension for me.

The literature for it says it treats:

Safe-Guard Canine Dewormer will treat Roundworms, Hookworms, Whipworms, and Tapeworms.

But the active ingredient, Fenbendazole, is approved in Europe for treatment of Giardia.

From the this site:

Fenbendazole (50 mg/kg SID for 3 to 5 days) is effective in eliminating Giardia infection in dogs.  Fenbendazole is approved for Giardia treatment in dogs in Europe, and available experimental evidence suggests that it is more effective than metronidazole in treating Giardia in dogs.

From the sounds of it, fendendazole is not only available at lower cost, and over the counter, but it is considered safer and more effective in giardia treatment and precention:

Metronidazole is the most commonly used extra-label therapy; however, efficacies as low as 50% to 60% are reported. Safety concerns also limit the use of metronidazole in dogs and cats.

More on fenbendazole based anti parasitics here:

http://www.veterina rypartner. com/Content. plx?P=A&A=1596

More on fenbendazole and giardiasis on the Veterinary Information Network: com/VINDBPub/ SearchPB/ Proceedings/ PR05000/PR00425. htm


Fenbendazole (Panacur), well known for its effectiveness against a variety of intestinal parasites, also appears to be very effective against Giardia. In a controlled trial at Cornell 6/6 dogs were effectively treated. The same dose that is used to treat roundworms, hookworms, whipworms, and the tapeworm Taenia pisiformis (22 mg/lb orally once daily for 3 consecutive days) is used to treat Giardia. If the infection is not cleared on this regimen, a longer course of therapy is used (5 to 7 days). Fenbendazole has a proven track record for being very safe and is thought to not have any teratogenic effects. Fenbendazole is therefore the drug of choice for treatment of Giardia in pregnant animals.

Ironically, it’s also the treatment of choice (in conjunction with amoxicillin) for those pesky clostridium perfrigens, the weird little pest that made my last litter so sick. If I’d just wormed them a week earlier with the exact drug I normally use anyways, I could have saved almost $600 in vet bills and lab test fees. Figures!!